Investigation of multiferroic magnetic systems by ultrasonic velocity measurements

我们主要对同时具有反铁磁性、铁电和铁弹性的多铁化合物的研究感兴趣。除了基本的科学意义外，这类磁电材料(表现出其磁性和铁电性质之间的耦合的材料)可能被用作未来电子存储设备中控制磁化的替代手段，以及用于致动器、开关和磁场传感器。最近的研究结果引发了人们对这一领域的兴趣，这些结果表明，由于磁场受挫而有利于非共线自旋组态的三角形晶格反铁磁体是观察强磁电效应的良好候选者。因此，本研究的目标是在CuO(T=230K)和BiFeO(T=643K)的情况下，研究一系列受挫的多铁化合物的磁性、铁电和弹性性质，这些化合物在低温甚至高温下表现出由于螺旋磁结构的稳定而产生的铁电性。我们的实验室提供了一种灵活的方法来研究单晶在液压作用下的弹性性质随温度和磁场的变化。我们是世界上少数几个能够在很大范围内(2-300K、0-15特斯拉和0-15千巴)测量弹性性质和相图随这三个外部参数的函数的小组之一。我们的方法有可能获得重要的结果，以便澄清在这类化合物中观察到的弹性、电和磁性之间耦合的性质。这些结果也将为我们课题组开发的理论模型提供指导。因此，这项工作应有助于更好地了解磁电化合物的性质，并可导致开发用于技术应用的新材料。

We are principally interested in the study of multiferroic compounds which are simultaneously antiferromagnetic, ferroelectric, and ferroelastic. Besides the fundamental scientific interest, this class of magnetoelectric materials (materials that show a coupling between their magnetic and ferroelectric properties) can potentially be used as an alternative means for controlling the magnetization in future electronic memory devices, as well as for actuators, switches, and magnetic field sensors. The interest in this field has been trigger by recent results which suggest that triangular lattice antiferromagnets, which favour non-collinear spin configuration due to magnetic frustration, are good candidates for the observation of strong magnetoelectric effects. Thus, the objective of this program of research is to investigate the magnetic, ferroelectric, and elastic properties of a series of frustrated multiferroic compounds which display ferroelectricity induced upon the stabilization of a helical magnetic structure at low or even high temperatures in the case of CuO (T = 230 K) and BiFeO3 (T = 643 K).The fundamental elastic properties of this class of materials are accessed using high resolution ultrasonic velocity measurements. Our laboratory offers a flexible way to investigate the elastic properties of single crystals under hydraulic pressure as a function of temperature and magnetic field. We are one of the few groups in the world capable of measuring elastic properties and phase diagrams as a function of these three external parameters over a wide range (2 - 300 K, 0 - 15 Tesla, and 0 - 15 kbar). Our approach holds potential for the acquisition of significant results in order to clarify the nature of the coupling between elastic, electric, and magnetic properties observed in this family of compounds. These results will also provide guidance for theoretical models developed by our group. This work should therefore contribute to a better understanding of the properties of magnetoelectric compounds and could lead to the development of new materials for technological applications.